Life in the extreme environment of a polar ocean certainly is a survival challenge, but some Antarctic fish manage with ice water in their veins — literally.

In Antarctica’s coastal waters, a group of perch-like fish called icefish dominates. The water column in these frigid seas is filled with tiny ice crystals, and fish are constantly exposed to ice through their gills and skin. They even ingest ice crystals when they eat and drink.

For years, scientists believed all sponges were filter feeders that trapped and fed on bacteria from water they pump through their bodies. But in 1995, researchers discovered that certain species of sponge enjoy meatier meals.

There’s a massive meltdown happening in the Arctic — and it’s not just polar bears who will feel the effects.

Since satellite monitoring began in 1979, sea ice in the Arctic has been on the decline, shrinking by about 10 to 12 percent per decade. In the summer of 2007, Arctic sea ice cover shrank to an unprecedented low. At this rate, researchers project that the Arctic may experience a summer completely devoid of ice by the end of the century.

Vast expanses of sea ice make the Arctic and Antarctic oceans perilous and inhospitable, but they’re also vital guardians of Earth’s climate.

Sea ice forms when ocean water is cooled to the freezing point by cold polar air. Freezing begins in fall, when the amount of light from the sun decreases, and ice continues to expand and thicken during the dark winter months. When summer returns, the sun’s energy warms the surface of the ice, causing portions of it to melt.

You might imagine marine snails crawling around on the sea floor. But thanks to a unique adaptation, one family of snails lives life at the top of the ocean.

Violet snails cannot swim but they can construct “rafts” from clusters of air bubbles, and these rafts allow the snails to float at the water’s surface. They float throughout tropical and subtropical oceans, preying on an abundant food source − jellyfish.

If you think a fish out of water would be easy to catch, you haven’t encountered the Pacific leaping blenny.

This acrobatic, slippery little fish can be found hopping and climbing around the rocky coasts of Guam. A diminutive 1½ to 3 inches in length, it spends almost all of its time on land — a curious and unique lifestyle among marine fish. To navigate its rocky habitat, the blenny has developed a tail-twisting move that allows it to leap from rock to rock with impressive distance and agility.

Wind and gravity aren’t the only forces that move the ocean’s water — there’s also a conveyor belt at work.

The Great Ocean Conveyor works by thermohaline circulation — water movement caused by density differences. The oceans are layered in water masses that differ in temperature and salt content. Lower temperatures and higher salinity translate to greater density.

Imagine a Komodo dragon the size of a large whale and you've got a rough picture of the mosasaur, one of the most fearsome predators in the oceans' history.

Top ocean predators of their time, mosasaurs were a group of carnivorous marine reptiles that lived during the Cretaceous period, roughly 90 million to 65 million years ago. Mosasaurs are thought to be related to present-day monitor lizards, and their fossilized remains have been found in many parts of the world.